Holland (1985) states that both people and environments can be divided into six vocational personality types or some combination of the six types: Realistic (outdoors, mechanical), Investigative (science, math), Artistic (art, language, music), Social (helping, teaching), Enterprising (selling, business) and Conventional (details, clerical). Holland's theory has had a tremendous impact on the fields of career counseling and interest assessment, and many interest inventories include scales that measure interests related to Holland's six types.
The Holland model is actually a "circle theory" with points on the circumference describing their similarity to other points. This is shown below:
Holland proposes that work interest be expressed in terms of the three top scoring scales in this model (eg RIE for Realistic, Investigative and Enterprising in that order) and that the proximity of these points in the model is significant. Those lying adjacent to one another suggest consistency or convergence of interest while those distant from one another indicate tension.
In the example, we see that the R and I are adjacent and point to a somewhat introverted person who is at once observant and rather concrete (as opposed to abstract) in thinking. The third point, E, suggests a need to be in control and to influence others which is rather at variance with the preceding points. This may suggest work in agriculture which covers the realistic aspect, working in pest control which covers the investigation aspect and the running of a business which provides this service which, along with giving advice to farmers covers the enterprising aspect. It would be expected that the need to be a successful investigator will get in the way of the business aspect and vice versa as they rely on different mindsets.
It may be apparent from this example that a simple model can result in fairly complex results allowing "triangulation" of specific careers.
Measurement A number of instruments have emerged over the years which purport to measure the Holland types. Perhaps the best known is the Self-directed search (ADS) which assesses interest, experience, knowledge and proficiency on the six areas and results in a fairly complete analysis of the Holland type. Accompanying the SDS, a dictionary of occupational titles has been published which lists occupations in terms of their Holland code thus allowing a counselor to provide a list of possibilities to prospective students starting out on training for a career. Validity If it is possible to comment on the validity of a theory like this one, it appears that Holland has produced a model which seems to cover the whole area of work in a rather elegant way. It is possible to predict the Holland type of a subject using personality instruments. This is shown below.
Realistic
16PF: M- (Practical), A- (Aloof), Q3+ (Self-controlled)
Enneagram: Type IX : Mediator, Type V: The Observer
Investigative
16PF: N+ (Suspicious), B+ (Intelligence), Q3+ (Self-confident)
Enneagram: Type VI : Loyalist
Artistic
16PF: L+ (Imaginative), I+ (Sensitive), G- (Unconventional)
Enneagram: Type IV (Romantic)
Social
16PF: A+ (Warmhearted), F+ (Enthusiastic), I+ (Sensitive)
Enneagram: Type II (Giver) Enterprising
16PF: E+ (Assertive), O+ (Self-confident), H+ (Adventurous)
Enneagram: Type VII (Hedonist), Type VIII (Boss)
Conventional
16PF: G+ (Perfectionistic) Q3+ (Self-controlled), F- (Serious)
Enneagram: Type I (Perfectionist)
This suggests that construct validity is fairly high with moderate correlations across the board on this table. Furthermore, the face validity of the entire model remains high and there are few who do not understand the basic concept and its application fairly readily.
A foundation of motivation
What is a better source of motivation than interest in what you are doing? This single factor gives all the strength to the Holland model as it adequately predicts success in a cluster of occupations on just this: interest. Furthermore, the inherent relationship between interest and temperament lies in the fact that certain people are simply better suited to specific types of work. Examples of this are legion and do not really require mention. In a person's development, temperament develops as a life-style factor as do specific interests and preferences. The assessment of these as a solid predictor of work success must form and important and necessary part of assessment for any type of employment.
References
Holland, J.L. (1985). Making vocational decisions (2nd edition) . Englewood Cliffs, NJ: Prentice-Hall.